Multiwavelength observations of Sgr A. I. 2019 July 18

Joseph M. Michail*, Mark Wardle, Farhad Yusef-Zadeh, Devaky Kunneriath

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    12 Citations (Scopus)

    Abstract

    We present and analyze ALMA submillimeter observations from a multiwavelength campaign of Sgr A during 2019 July 18. In addition to the submillimeter, we utilize concurrent mid-infrared (mid-IR; Spitzer) and X-ray (Chandra) observations. The submillimeter emission lags less than δt ≈ 30 minutes behind the mid-IR data. However, the entire submillimeter flare was not observed, raising the possibility that the time delay is a consequence of incomplete sampling of the light curve. The decay of the submillimeter emission is not consistent with synchrotron cooling. Therefore, we analyze these data adopting an adiabatically expanding synchrotron source that is initially optically thick or thin in the submillimeter, yielding time-delayed or synchronous flaring with the IR, respectively. The time-delayed model is consistent with a plasma blob of radius 0.8 RS (Schwarzschild radius), electron power-law index p = 3.5 (N(E) ∝ E-p ), equipartition magnetic field of Beq ≈ 90 Gauss, and expansion velocity vexp ≈ 0.004c. The simultaneous emission is fit by a plasma blob of radius 2 RS, p = 2.5, Beq ≈ 27 Gauss, and vexp ≈ 0.014c. Since the submillimeter time delay is not completely unambiguous, we cannot definitively conclude which model better represents the data. This observation presents the best evidence for a unified flaring mechanism between submillimeter and X-ray wavelengths and places significant constraints on the source size and magnetic field strength. We show that concurrent observations at lower frequencies would be able to determine if the flaring emission is initially optically thick or thin in the submillimeter.

    Original languageEnglish
    Article number54
    Pages (from-to)1-7
    Number of pages7
    JournalAstrophysical Journal
    Volume923
    Issue number1
    DOIs
    Publication statusPublished - 10 Dec 2021

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